Method of producing chromium wearing surfaces



- ishing closely to size.

Patented Mar. 23, 1943 Mrrmoo F raonoomo CHROMIUM WEARING SURFACES Henderik Van der Horst, Hilversum, Netherlands, assignor, by mesne assignments, to Van der Horst. Corporation of America, a corporation of Delaware No Drawing; Appli'cationlApr'il 25, 1939, Serial This invention relates to chromium surface layers on wearing surfaces, 1. e., surfaces subject to friction, and especially cylinder bores;

279,018,1In Great Britain February 21, V '{1'r iaim (cram-2s) mium is removed from the surface, and the surface of the chromium after treatment is covered It is known that by providing a surface layer I of chromium on the cylinder bores of engines,

pumps, air compressors and the like the rate of wear of the bore can be very greatlyreduced as the chromium layer is extremely hard and is also highly resistant to corrosion.

The chromium layer can be deposited electrolytically on the cylinder bore, and owing to the hardness of the chromium it is desirable that the deposited chromium should be of such a form and thickness that a minimum of mechani- ,with small grooves, pits or depressions which.

under examination with a low-powered microscope have the appearance of cracks in the surface. After a longer treatment with the reversed current the grooved or lined appearance may disappear, the surface being well pitted however.

The appearance of the surface and-the effective area of the grooves, pits or depressions relative to the total area of the surface depend to a certain extent on the length of the treatment with reversed current and the current density cal finishing of the surface is required. It is also desirable that the finished surface ofthe chm-- mium should not be too smooth as a highly pol-, f

ished chromium surface is liable to pick up under working conditions, that is, to be torn away from a the surface of the cylinderbore'.

provided with a layer orcoating of chromium in the surface of which are formed numerous small grooves, pits or depressions. Under working, con- I ditions oil is retained in these and there is no tendency for the chromium to pick up. Further, such a finely irregular chromium surface permits the piston rings to grind the chromium layer sufficiently to form a close fit between therings preferably a chromic acid solution as used in the and cylinder early in their life, despite the extreme hardness of chromium as a metal, and

also permits the face of a chromium layer to be, i

worked reasonably readily, for example for fin- 1 It is not to be understood however that 'the chromium must be pitted or perforated to the underlying metal (e. g. cast-iron).- Preferably at least the chromium layer is aifected only part way through, the layer as a whole being impervious.

In a preferred method of forming these grooves, pits or depressions a layer of chromiumof the desired thickness or of slightly more than the required thickness is deposited electrolytiduce friction.

employed, and afterv a prolonged treatment the surface may have the appearance of' an open grain cast'iron.

The treatment of the chromium with reversed :current, i. e. with current flowing insuch a direction that the chromium serves as an anode,

may be carried out in the samebath as the depo- According to my invention a. cylinderbore is sition of the chromium but preferably it is ,car-

ried out in a separate bath to avoid spoiling the solution. The solution in the second'bath is first bath, but various other acid or alkaline solutions such as a 20 caustic soda solution may be employed.

Experiments have shown that a suitable surface can be obtained by treating a smooth chromium deposit with a reversed current of from 150 to 450 ampere-minutes per square fdecimetre.

In addition to their function ofretaining oil the grooves, pits or depressions in the surface of the chromium reduce, the effective area of the surface which is in contact with'a piston or other member working in the cylinder bore and sore- Further, the reduction in the effective surface area facilitates any honing or grinding of the surface which may be subsequently carried out to bring it exactly to size as there is less chromium to remove.

cally on the cylinder bore by the process de- 5 chromium of such thickness that the internal scribed in Patent No. 2,048,578 employing an aqueous chromic acid bath or solution as described therein and an anode of circular crosssection and of a diameter only slightly less than that of the cylinder bore; it is not essential howtreatment is that a certain amount of the chro- As a certain amount of chromium is removed when the surface is treated with a reversed cure a rent it is desirable in depositing the chromium v initially on a cylinder bore to deposit a layer of inder, cylinder block or liner of cast-iron or other metal suitable for the foundation and having a bore somewhat oversize, and plate it with chromium electrolytically until its diameter is less than the diameter desired when finished, for

example say about one thousandth of an inch less; then I apply the reversed current treatment until the surface of the chromium is well pitted or porous; and then I hone the treated surface to the size desired, usually using first a rough bone and then a finer one to finish.

To avoid excessive removal of chromium from the deposited layer at the ends of the cylinder bore when the current is reversed, cylindrical extensions having the same diameter as the cylinder bore may be temporarily secured to the ends of the cylinder block or liner in alignment with the bore.

If desired the surface of the chromium layer after deposition maybe lightly honed to remove any projections or high spots before the chromium is treated with the reversed current.

A chromium surface in accordance with my invention is particularly adapted for use in the cylinders of engines having aluminium pistons and can be applied to cylinder blocks, barrels or liners of cast-iron, steel or any other metal on which chromium can be deposited electrolytically, and it can also be applied to other cylin- I drical bores.

pumps, compressors and the like, it can be applied to other chromium plated members tending to wear by frictional contact, where the retention of lubricating oil between the contacting members is desirable, or Where the applied chromium is liabl to be picked up, etc.

' I claim:

1. The process of producing grooves, pits or depressions in an electrodeposited chromium wearing surface of a wearing member, which consists in passing current through the surface of the electrodeposited chromium for a short time, in an electrolytic bath adapted to remove chromium from such surface and in such a di rection that the chromium at such surface is an anode, until at least about 150 ampere-minutes of electricity per square decimeter. of the surface, but less than sufficient to completely remove the chromium,. has passed through such surface, there being taken thereafter no electrolytic action closing with metal the grooves, pits or depressions produced by the action of said current. I

2. The process of producing on the wearing face of a member subject to wear a layer of chromium in the surfac of which are grooves, pits or depressions, which consists in electrolytically depositing a layer of chromium on said face, and

after said layer has been completely deposited,

passing current through said layer for a-short time, in an electrolytic bath adapted to remove chromium from the surface of the layer and in such a direction that the surface of said layer is an anode, until between about 150 ampereminutes-and about 450 ampere-minutes of electricity per square decimeter of the chromium surface, has passed through the chromium sur face, to remove electrolytically a part of the deposited chromium.

3.. The process of producing on a wearing member a wearing face of chromium in the surface of which are grooves, pits or depressions, which consists in electrolytically depositing a layer of chromium on said member, and after said layer has'been completely deposited, passing current through said layer for a short time, in an aqueous electrolytic bat-h adapted to remove chromium from the surface of the layer and in ill such a direction that the surface of the layer is an anode, until at least about -ampere-minutes of electricity per square decimeter of the surface, but less than sufficient to completely remove the chromium, has passed through such surface, and thereafter removing mechanically a portion of the surface containing the grooves, pits or depressions which result from the action of said current.

4. In the manufacture of bores, the steps in the method which consist in taking a bore of a foundation metal having a diameter greater than the desired finished diameter, electroplating the same with chromium to a thickness such that the diameter of the bore is substantially equal to or is less than the desired finished diameter, and thereafter passing current through the chromium for a short time, in an aqueous solution of an electrolyte adapted to remove chromium from the surface and in such a direction that the exposed surface of the chromium is an anode, until at least about 150 ampere-mix .utes of electricity per square decimeter of the surface of the chromium has passed through the chromium, to remove electrolytically a part of the deposited chromium and produce therein grooves, pits or depressions.

5. In the manufacture of bores, the steps in the method which consist in taking a bore'of a foundation metal having a diameter greater than the desired finished diameter, electroplating the same with chromium to a thickness such that the diameter of the bore is less than the desired finished diameter, thereafter passing current through .the chromium for' a short time, in an electrolytic bath adapted to remove chromium from the electroplate and in such a direction that the chromium is an anode, and until at least about 150 ampere-minutes of electricity per square decimeter of the surface of the chromium has passed through the chromium, to produce grooves, pits or depressions in the chromium, and thereafter treating the bore by an operation similar to honing to enlarge the bore to the desired finished diameter.

6. The subject matter of claim 1, characterized by the fact that the electrolytic bath is an aqueous solution of chromic acid.

'7. The subject matter of claim 1, characterized, by the fact that the electrolytic bath'is an aqueous solution of caustic soda.

8. A process for producing on the surface of the bore of a cylinder a layer of chromium in the I surface of which are grooves, pits or depressions,

consisting in electrolytically depositing a layer of chromium on the bore and then treating the bore for a short time, in an electrolyte adapted to remove chromium from the layer, with a current insuch a direction that the chromium layer is an anode until from about 150 to about 450 ampere-minutes of electricity per square decimeter of the surface of the layer has passed in said direction.

9. A process as claimed in claim 8 in which the treatment with the chromium layer acting as an anode, is carried out in an aqueous chromic acid solution separate from the bath in which the chromium is deposited.

10. A process as claimed inclaim 8 in which the treatment with the chromium layer acting as an anode, is carried out in an aqueous alkaline solution separate from the bath in which the chromium is deposited.

11. A process for producing on the bore of a cylinder a layer of chromium in the surface of current in such a direction that the chromium layer is an anode until at least 150 ampere-min-' utes of electricity per square decimeter oi the surface of the layer has passed through said surface but for less than suflicient time to completely remove the chromium layer,.--to produce in the chromium layer the aforesaid grooves, pits or depressions.

HENDEBIK VAN nun HORST. 

